/Engine/Source/Runtime/AudioMixer/Public/AudioMixerDevice.h
If SoundSubmix is a soundfield submix, this will return the factory used to encode source audio to it's soundfield format. Otherwise, returns nullptr.
[ISoundfieldFactory](API\Runtime\AudioExtensions\ISoundfieldFactory) * GetFactoryForSubmixInstance ( [USoundSubmix](API\Runtime\Engine\Sound\USoundSubmix) * SoundSubmix )